1. Field of Application
The invention relates to nonferrous metallurgy, in particular to the manufacture of graphitized products such as electrodes for electric steelmaking, slabs for blast and titanium-magnesium production furnaces, anodes for the chemical industry, and to reducing processes in nonferrous and ferrous metallurgy.
2. Description of the Prior Art
There is known a carbonaceous heat insulating charge used for thermal processing of carbon and carbon graphite products in electric resistance furnaces comprising 60% by volume of fine metallurgical coke sized 0 to 10 mm of which 12% by mass is ash, and 3% by mass is, volatiles. In addition, the known charge contains 30% by volume of quartz sand and 10% by volume of sawdust.
A shortcoming of said charge is the presence of quartz sand which forms silicon carbide at a temperature of about 2000.degree. C., chemically reacting with the furnace refractory lining and causing the failure thereof. Silicon carbide also affects adversely the chemical reactivity of the charge and increases its both ash content and heat conductivity.
Furthermore, silicon inhibits pore formation in the charge, this preventing the complete removal of gases from the furnace space which gases increase the ash content in products and thus impair their quality.
There is also known a carbonaceous heat insulating charge comprising 70 to 83 percent by volume of coke sized 0 to 10 mm with 12% by mass of ash and 3 percent by mass of volatiles and 17 to 30 percent by volume of sawdust.
A shortcoming of said charge is such a large proportion of sawdust sharply increases the heat conductivity of the charge due to a substantial formation of pores in course of graphitization. The increase in the charge heat conductivity results in a greater specific consumption of electric power and a consequent reduction in the efficiency of the furnace by 20 to 30 percent. A higher heat conductivity also raises the temperature gradient across the body of items involved and so promotes a greater crack formation, this resulting in a higher amount of discards.
There are also known reducing agents used in nonferrous metallurgy, e.g. in the manufacture of titanium tetrachloride which are formed of cokes such as pitch or various petroleum refinery cokes (e.g. pyrolysis coke, cracking coke, formed coke in slow coking plants), anthracite, gas coal and charcoal.
Any of these reducing agents must comply to general performance requirements, namely high reactivity, low electrical conductivity, and low ash content and cost.
Petroleum and pitch cokes are most efficient reducing agents. These cokes contain substantial amounts of carbon (80 to 90%) and have low ash content. However, they have found no practical application due to both their high cost and high electric resistance (.rho.=5000 ohm mm.sup.2 /m). On the other hand, inexpensive pertroleum coke, obtained in slow coking plants, has found no practical application due to its high volatile (up to 9% by mass) and moisture (up to 12% by mass) content and excessive electric resistance (.rho.=8000 ohm mm.sup.2 /m) causing high consumption of electric power.
The anthracite used in smelting titanium slags is low in reduction capacity due to its poor reactivity and so is required in large amounts. Anthracite also has a high electric resistance (.rho.=8000 ohm.mm.sup.2 /m), rather high contents of ash (up to 1.7% by mass), high volatiles (up to 9% by mass), high moisture (up to 12% by mass) and high sulfur (up to 1.0% by mass), all of which slow down reduction and otherwise adversely effect smelting (splashing due to a high moisture content), and the resulting product (increased amount of impurities in the resultant product). Finally, the anthracite is a costly reducing agent.
It is therefore an object of the present invention to provide a charge for use in graphitization furnaches, which will make it possible to improve the quality of graphite products.
Another object of the invention is to provide a charge for use in graphitization furnaces, whose production cost is lower than that of any of the known charges.
Still another object of the invention is to provide such a charge which, after being used in the graphitization process, is still suitable for use in ferrous and non-ferrous metallurigical reduction processes, where it possesses a higher reactivity, lower electric resistance and is purer in chemical composition than known reducing agents.
The above and other objects of the invention are attained by providing a charge for use in graphitization furnaces consisting of coke and sawdust, which, in accordance with the invention, consists of 85 to 95 percent by mass of coke comprising not less than 90 percent by volume of size fraction ranging from 0.5 to 2 mm and not more than 10 percent by volume of size fraction ranging from 2 to 10 mm and of 5 to 15 percent by mass of sawdust.
The invention makes it possible to increase the yield of sound products up to 100 percent as against the previously attained 95 percent. The cost of the charge of the invention is 20 percent lower than that of the known charges. In addition, the invention has made possible the use of metallurgical and petroleum cokes of any known contents of ash and volatiles, including cokes previously not used due to high contents of ash and volatiles.
The invention also provides a reducing charge composed of 85 to 95 percent by mass of coke containing not less than 90 percent by volume of a size fraction ranging from 0.5 to 2 mm and not more than 10 percent by volume of a size fraction 2 to 10 mm, and of 5 to 15 percent by mass sawdust, which has been thermally processed at a temperature of not less than 2000.degree. C. in the course of graphitization.
The invention has provide a solution to the problem of economizing on coke, a scarce carbonaceous material by more efficiently using readily available, although previously thought unsuitable, materials. Further economy is attained, according to this invention, by employing the reducing properties of the charge after use in the graphitization furnace in nonferrous and ferrous metal metullurgy. The graphitization charge is highly reactive and reduces by 77.3 percent the consumption of electric power in the manufacture of titanium tetrachloride. In addition, the charge intended as a reducing agent has a low electric resistance (.rho.=95.5 to 243 ohm mm.sup.2 /m), this also providing an economy in the use of electric power. The proposed reducing charge is cheap, since it is substantially a product already spent in the electrode manufacture and requires no special processing. The proposed reducing charge contains, % by mass: volatiles, 0.3 to 1.28; ash, 0.3 to 12.; sulfur, 0 to 0.3; moisture, 0.0 to 3.0.